SEROTONIN AND NADPH-DIAPHORASE IN THE DORSAL RAPHE NUCLEUS OF THE ADULT-RAT

NADPH-diaphorase histochemistry, employed as a marker for nitric oxide synthase (NOS), was combined with serotonin (5-HT) immunofluorescence to investigate the relationship between NOS and 5-HT in the rat dorsa l raphe nucleus. Many NADPH-diaphorase labelled cells and varicose axo ns were observed in the nucleus. Coexistence between NADPH-diaphorase and 5-HT occurs in cells of the dorsomedial and ventromedial subgroups but not in the lateral subgroups. Coexistence was not observed in axo ns, but NADPH-diaphorase labelled axons contact 5-HT/NADPH-diaphorase containing cell bodies. These findings have implications for the role of nitric oxide in 5-HT pathways and for the mechanism of action of 5- HT neurotoxins.